MTN SHEESA 600 SEEMS LIKE A ****

I took out Sheesa 600 home internet. I am supposed to get 300gb on full speed, then 300 gb on 20mbps. However, month after month they shut me right down to 0.3mbps, even though their app says I still have 30 gb left of the FULL SPEED bundle. I don't even get the 20mbps bundle. This always happen around the 20th, I get an sms saying they are throttling me, then it happens. When I phone, I get told it must be just a mistake, as I am well within my limits, however nobody can fix it and nobody is intetested. So every month I cannot watch ANY TV for the last 10 days. We do not download we only watch Netflix and other streaming and not excessively. When I was on fibre we never exceeded 150gb per month.